Some conventional engines (internal combustion engines) have two parallel modes of cylinder injection (direct injection (DI)) and port injection. The engines perform homogeneous combustion in the cylinder having a uniform concentration distribution of air-fuel mixture therein, and stratified combustion in the cylinder containing dense air-fuel mixture concentrated around a spark plug in a layered form.
The typical fuel injection control mainly involves the port injection during the homogeneous combustion, and the direct injection during the stratified combustion. The selection of an appropriate fuel injection mode depending on the operating state of an engine and the load thereon can improve the fuel economy while maintaining the output of the engine and combustion stability.
While a port injector is provided inside the intake port of each cylinder, direct injector is provided such that its exit protrudes into the combustion chamber of each cylinder. This may cause accumulation of deposits around the exit of the direct injector, thereby inhibiting proper direct injection. For example, the accumulated deposits may reduce the opening area of the exit to decrease the volume of direct injection, or may vary the direction or shape of fuel spray to deteriorate the combustion characteristics of air-fuel mixture.
Under such circumstances, techniques have been disclosed for removing the deposits accumulated on the direct injector by forced direct injection. For example, Patent Literature 1 discloses a control for forcibly varying the fuel injection mode to perform only direct injection even in the operation region for port injection. If a reduction is determined in the volume of fuel injection from the direct injector, this technique forces the direct injector to perform direct injection by predetermined combustion cycles, even during the port injection. This control operation can remove the deposits accumulated around the exit of the direct injector by blowing off.